In this research, acute toxicity (LC) of zinc oxide nanoparticle on Beluga (Huso huso) andcommon carp (Cyprinus carpio) was studied. The experiment was conducted using theOrganization for Economic Co-operation and Development (No. 202) method. For bothspecies, 96hLC10 was determined to be more than 200 mg/l. To assess the effects of zinc oxidenanoparticles on blood factors, leukocyte index count (Lymphocyte, Monocytes, Neutrophils,Eosinophil, and Basophils) was performed, and the results were analyzed using IBM SPSSsoftware version. According to the results and based on the ANOVA test, there is no significantdifference among mean values of leukocyte index responses (p>0.05), and one should notethat the amount of lymphocyte had decreased while that of neutrophils and monocytes hadincreased. Furthermore, with regard to concentration levels, this decrease or increase has notfollowed a systematic trend. In Beluga based on ANOVA test, there is a significant differencebetween mean values of lymphocytes and neutrophils (p<0.05). Again, compared to control,lymphocyte count increased while that of neutrophils and eosinophil decreased, and this too, didnot follow a systematic trend. Finally, concentration to 200 mg/l ZnO did not cause mortality inHuso huso and Cyprinus carpio. Eventually, decline of body resistance against nano zinc oxidewas observed in these species through blood cells study.